1. Field of the Invention
The present invention relates to a light-and-shade inspecting apparatus and method for inspection of a low contrast light-and-shade defect, such as a contaminant, cloudiness etc., on a plain material roll (or web) such as a paper, film and nonwoven fabric, etc., based on an image data which is produced by an image pick-up device picking up the web having a certain width and traveling in one direction.
More particularly, the light-and-shade inspecting apparatus and method also are capable of distinctly judging between a low contrast defect as a shade defect or a light defect.
2. Description of the Related Art
FIG. 4 is a block diagram showing a conventional light and shade inspecting apparatus 11, as disclosed in Japanese (examined) Patent Publication No. 7-99355, for detecting low contrast light and shade.
The light-and-shade inspecting apparatus 11 includes an area sensor portion 13, a brightness information adding portion 15 coupled to an output of the area sensor portion 13, an amount of change calculating portion 17 coupled to an output of the brightness information adding portion 15, a detecting portion 11 coupled to an output of the amount of change calculating portion 17, and a display portion 21 coupled to outputs of the area sensor portion 13, adding portion 15, amount of change calculating portion 17 and detecting portion 19.
The area sensor portion 13 picks up an image of a web as an object to be inspected, and obtains brightness information of each pixel of a plurality of pixels arranged in a two-dimensional. array.
The brightness information adding portion 15 is adapted for sectioning (e.g., dividing) the two-dimensional array of pixel brightness information, which is obtained through the area sensor portion 13, into a plurality of grids of rows and columns of pixels, and then obtaining an added value at each grid by adding together brightness information of the respective pixels within each grid.
The amount of change calculating portion 17 is adapted for obtaining horizontal and vertical changes in an amount of the brightness added value between each pair of grids and within a range of 3 rows and 3 columns of each grid. More particularly, the amount of change calculating portion 17 performs a difference processing or differential processing so as to form a differentiating filter.
The detecting portion 19 is adapted for detecting a mottle (e.g., a low contrast light-and-shade portion such as a mark, streak, blotch, etc.) on the web based on the vertical and horizontal changes in an amount of the brightness.
With the conventional light and shade inspecting apparatus, a low contrast light-and-shade portion such as a contaminant, cloudiness, etc., on the web, can be detected. However, the differential processing is performed in the amount of change calculating portion and then, based on the resultant value sizes, a low contrast light-and-shade defect is detected. Therefore, it is impossible to judge whether the defect thus detected is a light defect or a shade defect.
Moreover, erroneous detection of one defect as two defects may occur since a portion (e.g., an end) of the defect may surge and sag in its differentiated value through the differential processing thereof. Thus, one defect could be erroneously detected as two defects, thereby erroneously raising the total number of defects present on the web.
In view of the foregoing and other problems of the conventional apparatuses and techniques, an object of the present invention is to overcome the conventional problems and to provide a light-and-shade inspecting apparatus and a light-and-shade inspecting method, which allow low contrast defects to be precisely detected by distinguishing light and shade from each other and without mistaking only one defect for two defects.
To achieve the above and other objects, in a first aspect, a light-and-shade inspecting apparatus according to the present invention for picking up an image of an object to be inspected, and then, based on such image data, inspecting a light and shade on the object, includes:
an image pick-up device for picking up an image of the object to output an image data;
an integrated image calculating portion for dividing the image data outputted from the image pick-up device into a mesh pattern of meshes which are equivalent in area to each other and then adding together the image data within each of the divided meshes to obtain an integrated image;
a differentiated image calculating portion for performing a difference (e.g., differential) operation between each pair of meshes apart by a predetermined interval from each other with respect to their corresponding two integrated images obtained through the integrated image calculating portion;
a defect detecting portion for comparing a value obtained through differentiated image calculating portion with a predetermined value to detect a defect a portion which is partially different in lightness from other portions on the object;
an average value calculating portion for calculating an average value of the integrated image obtained through the integrated image calculating portion; and
a light-and-shade judging portion for judging whether the defect detected by the defect detecting portion includes a light defect or a shade defect based on the average value obtained through the average value calculating portion and values of the integrated images in the predetermined pairs of meshes apart a predetermined interval from each other which have been subjected to the difference operation.
Additionally, in the light-and-shade inspecting apparatus according to the present invention, the light-and-shade judging portion functions to subtract the average values of the integrated images in the predetermined pairs of meshes apart from each other from the values of the integrated images to produce the respective subtracted values, and, when one of the subtracted values is larger in absolute value than another of the subtracted values and that the subtracted value in connection with the mesh corresponding to the one of the subtracted values is larger than zero (0), judges the defect in the mesh corresponding to the one of the subtracted values to be a light defect.
Furthermore, in the light-and-shade inspecting apparatus according to the present invention, the light-and-shade judging portion functions to subtract the average values of the integrated images in the predetermined pairs of meshes apart from each other from the respective values of the corresponding integrated images to produce the respective subtracted values, and, when one of the subtracted values is larger in absolute value than another of the subtracted values and that the subtracted value in connection with the mesh corresponding to the one of the subtracted values is negative, judges the defect in the mesh corresponding to the one of the subtracted values to be a shade defect.
In a second aspect of the present invention, a light-and-shade inspecting method, includes:
picking up an image of an object to obtain an image data;
dividing an image composed of the image data into a mesh pattern of meshes which are equivalent in area to each other and then adding together the image data within each of the divided meshes to obtain an integrated image;
performing a difference operation between each pair of meshes separated by a predetermined interval from each other with respect to their corresponding two integrated images to obtain a differentiated image;
comparing a value obtained from the differentiated image with a predetermined value to detect as a defect a portion which is at least partially different in lightness from the other on the object;
calculating an average value of the integrated image; and
judging whether the defect includes a light defect or a shade defect based on the average value and values of the respective integrated images in each pair of meshes apart a predetermined interval from each other which have been subjected to the difference operation.
Thus, unlike the conventional apparatus, the present invention precisely detects low contrast defects by distinguishing light-and-shade from each other and without mistaking a single defect for two defects.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 10-205252, filed Jul. 21, 1998, which is expressly incorporated herein by reference in its entirety.